class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;
    TreeNode() {}
    TreeNode(int val) { this.val = val; }
    TreeNode(int val, TreeNode left, TreeNode right) {
        this.val = val;
        this.left = left;
        this.right = right;
    }
}


public class Text1 {
    public TreeNode invertTree(TreeNode root) {
        if (root==null) return null;

        TreeNode node = root.left;
        root.left=root.right;
        root.right=node;

        invertTree(root.left);
        invertTree(root.right);

        return root;
    }
}
